Caster plug



FIG. 1 is a top left front perspective view of a caster plug showing our new design;

FIG. 2 is a top left front perspective view thereof with the broken line showing of a caster being for illustrative purposes only and forming no part of the claimed design;

FIG. 3 is a top plan view thereof;

FIG. 4 is a left side elevational view thereof; the opposite side being a mirror image;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is a front elevational view thereof; the rear elevational view being a mirror image. 

The ornamental design for a caster plug, as shown and described. 